Method for making aromatic polyformals

ABSTRACT

A method is provided for making linear film forming aromatic polyformals having a reduced percent by weight of aromatic polyformals in the cyclic state. Reduced cyclic polyformal content in the linear aromatic polyformal is achieved by a filtration of the reaction product of a bisphenol and methylene halide in the presence of an alkali metal hydroxide, followed by the addition of an antisolvent to the reaction mixture to effect reverse precipitation.

BACKGROUND OF THE INVENTION

The present invention relates to a method for making aromaticpolyformals. More particularly, the present invention relates to amethod for eliminating cyclic polyformal from film forming aromaticpolyformal.

As shown in copending application of Allan S. Hay, Ser. No. 889,393, nowabandoned, filed concurrently herewith and assigned to the same assigneeas the present invention, aromatic polyformal consisting essentially ofchemically combined units of the formula,

    --OROCH.sub.2 --, (1)

is made by reacting a bisphenol, methylene halide, alkali metalhydroxide in combination with a dipolar aprotic solvent, or in anorganic solvent utilizing a phase transfer catalyst, where R is aC.sub.(6-30) divalent aromatic radical defined more particularly below.It has been found that in the process of forming and recovering sucharomatic polyformal from the aforementioned reaction mixture, thearomatic polyformal often has a substantial percent by weight aromaticpolyformal in the cyclic state. In particular instances, the utility offilms derived from the film forming aromatic polyformal can be reducedas a result of the presence of cyclic aromatic polyformal; the films canbe hazy and have a reduced Notched Izod Impact value.

SUMMARY OF THE INVENTION

The present invention is based on the discovery that if the abovedescribed aromatic polyformal reaction mixture is filtered, prior to therecovery of the aromatic polyformal by standard precipitationprocedures, and an antisolvent such as acetone, methanol, or mixturethereof, is added to the filtrate in a controlled manner, followed bywashing the resulting precipitate with an acetone-methanol solventmixture, that aromatic polyformal can be recovered having as little as1% or less of aromatic polyformal in the cyclic state.

Radicals induced by R of formula I are, C.sub.(6-30) divalent aromaticradicals, for example, phenylene, tolylene, xylylene, naphthalene, etc.;halogenated derivatives of such divalent aromatic hydrocarbon radicals,such as chlorophenylene, bromotolylene, etc., divalent radicals, such as--R¹ QR¹, where R¹ is selected from C.sub.(6-13) divalent aromaticradicals, Q can be cyclohexyl, fluorenyl, --O--, --S--, ##STR1## and--C_(y) H_(2y) --and y is equal to 1 to 5 inclusive.

DESCRIPTION OF THE INVENTION

There is provided by the present invention, a method for making a filmforming aromatic polyformal consisting essentially of chemicallycombined units of formula (1) which is substantially free of aromaticpolyformal in the cyclic state which comprises

(A) agitating a mixture containing as essential ingredients bisphenol ofthe formula,

    HO--R--OH,                                                 (2)

methylene halide, alkali metal hydroxide and a member selected from theclass consisting of a phase transfer catalyst and a dipolar aproticsolvent, where there is utilized in the reaction mixture per mole ofbisphenol, more than 1 mole of methylene halide and greater than 2 molesof alkali metal hydroxide,

(B) diluting the resulting mixture of (A) with at least 0.5 part byweight of an inert organic solvent, per part of the mixture of (A)

(C) filtering the resulting solution of (B),

(D) while agitating the solution of (C), adding at least 0.5 part byweight of an antisolvent, per part of the solution of (C), to effect theprecipitation of aromatic polyformal, and

(E) recovering the aromatic polyformal from (D), where R is aspreviously defined.

Included by the bisphenols or mixtures thereof of formula (2) which canbe used in the practice of the method of the present invention, are

2,2-bis(4-hydroxyphenyl)propane (Bisphenol-A);

2,2-bis(4-hydroxyphenyl)hexafluoropropane;

4,4'-methylene(2,6-di-tert-butylphenol);

2,4'-dihydroxydiphenylmethane;

bis-(2-hydroxyphenyl)methane;

1,1-bis(4-hydroxyphenyl)ethane;

1,1-bis(4-hydroxyphenyl)propane;

2,2-bis-(4-hydroxyphenyl)pentane;

3,3-bis-(4-hydroxyphenyl)pentane;

4,4'-dihydroxybiphenyl;

4,4'-dihydroxy-3,3',5,5'-tetramethylbiphenyl;

hydroquinone;

resorcinol;

9,9'-bis(4-hydroxyphenyl)-fluorene

3,4'-dihydroxydiphenylmethane;

4,4'-dihydroxybenzophenone;

4,4'-dihydroxydiphenylether;

2,2'-(4-hydroxyphenyl)-1,1-dichloroethylene;

2,2-bis(4-hydroxy-3-methylphenyl)propane;

2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane;

1,1-bis(4-hydroxyphenyl)cyclohexane;

1,1-bis(4-hydroxy-3,5-dimethylphenyl)cyclohexane;

1,1-bis(4-hydroxy-3-methylphenyl(cyclohexane;

bis(4-hydroxy-3,5-dimethylphenyl)sulfone;

5-chloro-2,4'-dihydroxydiphenylsulfone;

4,4'-dihydroxytriphenyl ether;

4,4'-dihydroxy-2,5'-dimethyldiphenyl ether, etc.

Methylene halides which can be used in the practice of the inventionare, for example, methylene chloride, methylene bromide, chlorobromomethane, etc. Alkali metal hydroxides which can be employed in thepractice of the invention are, for example, potassium hydroxide whichcan be in the form of pellets, powder, etc., sodium hydroxide, etc.

In the practice of the invention, the aromatic polyformal can be made byeffecting contact at a temperature of 0° C. to 100° C. and preferably40° C. to 100° C., between methylene halide and bisphenol in thepresence of alkali metal hydroxide. Reaction can be conducted betweenexcess methylene halide and bisphenol until the latter has beencompletely reacted.

Reflux temperatures at atmospheric pressure or above atmosphericpressure can be used along with agitation of the mixture. Reactionbetween methylene halide and bisphenol in the presence of excess alkalimetal hydroxide can be accelerated by using a substantially inert,higher boiling, organic solvent in combination with methylene halide,such as a nonpolar or dipolar aprotic organic solvent. Nonpolar organicsolvents which can be employed in the methylene halide are, for example,chlorobenzene, dichlorobenzene, benzene, toluene, etc. In addition,there can be used dipolar aprotic solvents, such as N-methylpyrrolidone,sulfolane, dimethylsulfoxide, etc.

Experience has shown that when methylene halide is employed in theabsence of a dipolar aprotic solvent, effective results are achieved ifa phase transfer catalyst is used to facilitate in situ formation of thealkali salt of the bisphenol and the subsequent condensation reactionwith the methylene halide. Suitable phase transfer catalysts are, forexample, quaternary ammonium and phosphonium salts, such as described inJACS 93, 195 (1971) by C. M. Starks. A proportion of from about 0.01 to2.0 moles of the phase transfer catalyst per mole of the bisphenol hasbeen found to provide for effective results, and preferably from 0.02 to0.10 moles of phase transfer catalyst per mole of bisphenol can beemployed.

The intercondensation reaction can be conducted over a period of from0.1 hours to 24 hours or greater depending upon such factors as thenature of the methylene halide, whether an organic solvent is employedin combination with the methylene halide, the type of such organicsolvent, temperature of the reaction, the degree of agitation, etc. Inparticular instances, for example, the more highly reactive methylenebromide can be substituted for methylene chloride or a mixture ofchlorobenzene with methylene chloride will reflux at a highertemperature. In addition, the reaction can be conducted at elevatedpressures, or in a closed system to permit the methylene halide to reactwith the bisphenol at a higher temperature. Those skilled in the artwould know, for example, that the methylene halide itself, when used inexcess amounts, can serve as a suitable organic solvent as well as areactant.

If desired, a chain-stopper can be employed in combination with thebisphenol and the methylene halide to control the molecular weight ofthe resulting aromatic polyformal. Suitable chain-stoppers which can beused are, for example, phenol, 4-methylphenol, 4-tert-butylphenol,3-chlorophenol, 2-methylphenol, etc. The chain-stoppers can be employedat from 0.001 to 0.1 moles of chain-stopper, per mole of bisphenol.

At the termination of the reaction, the mixture can be diluted with aninert organic solvent, which can include the nonpolar organic solvent,the dipolar aprotic solvent, or mixtures thereof as previously defined.There can be used from about 0.5 to 100 parts or more of inert organicsolvent, per part of reaction mixture. The resulting aromatic polyformalsolution having an intrinsic viscosity in chloroform at 25° C. of from0.3 dl/g to 2.0 dl/g, can be filtered of solids, such as alkali metalhalides.

Reverse precipitation of the aromatic polyformal from the clear polymersolution can be achieved by adding a precipitating solvent to thepolymer solution while it is being highly agitated. Suitableprecipitating solvents include, for example, acetone, methanol, mixturesthereof and other inert organic solvents in which the aromaticpolyformal is highly insoluble. There can be used from about 0.5 to 100parts or more of precipitating solvent per part of clear polymersolution.

It has been found that the aromatic polyformal can be isolated as aparticulate having a high bulk density, such as 0.2 to 0.25 g/ml, asdistinguished from the product obtained which can have a bulk density offrom 0.05 to 0.07 g/ml and be stringy rather than in a particulate form.It has been found that under reverse precipitation conditions, lineararomatic polyformal can be isolated having as little as from 3 to lessthan about 1 percent by weight of cyclic aromatic polyformal, based onthe weight of the aromatic polyformal.

The substantially cyclic-free aromatic polyformal has been found to beconvertible to clear films having valuable impact properties by standardcasting and molding procedures. These aromatic polyformal films can befabricated to high performance plastic parts by standard injectionmolding techniques exhibiting impermeability to moisture.

In order that those skilled in the art will be better able to practicethe present invention, the following examples are given by way ofillustration and not by way of limitation. All parts are by weight.

EXAMPLE 1

A mixture of 30 parts of 2,2'-(4-hydroxyphenyl)-1,1-dichloroethylene, 82parts of N-methyl-2-pyrrolidone, 80 parts of methylene chloride and 7.8parts of sodium hydroxide pellets was stirred and refluxed at atemperature of about 70° C. for 90 minutes. There was then added to themixture an additional 1.3 part of sodium hydroxide pellets and 0.145part of p-tert-butylphenol in the form of a 5% solution in methylenechloride. The reaction mixture was then refluxed an additional 90minutes. Termination of the reaction was achieved by allowing themixture to cool to room temperature and diluting it with 495 parts ofmonochlorobenzene. The mixture was then filtered through Hyflo®-Supercelto remove sodium chloride. The clear polymer solution was thenvigorously agitated while there was gradually added a 450 part mixtureof substantially equal parts by weight of methanol-acetone containingabout 1% by weight of acetic acid. There was obtained a precipitatewhich was collected by filtration and reslurried in methanol. Thesuspension was then filtered and the product dried in vacuo at 60° C.

Based on method of preparation, the product was a polyformal consistingessentially of chemically combined units of the formula, ##STR2## havingan intrinsic viscosity of 0.56 dl/g in chloroform at 25° C. The productwas found to have about 1% by weight of polyformal in the cyclic statebased on gel permeation chromatographic analysis. The yield of theproduct was about 75%. The product was converted to a clear film bymolding it at 150° C. and 5000 psi for 2 minutes.

EXAMPLE 2

A mixture of 35.35 parts of bisphenol-A, 0.459 part ofp-tert-butylphenol, 82.5 parts of methylene chloride and 95 parts ofanhydrous N-methylpyrrolidone was stirred under nitrogen. There wasadded to the mixture, 16.98 parts of sodium hydroxide pellets. Themixture was refluxed for 5 hours. An aliquot was removed (sample A) andanalyzed by liquid chromatographic analysis. Another aliquot was removed(sample B) which was added directly to methanol. The remainder of themixture was diluted with chlorobenzene to produce a 5% solution. Thissolution was then reverse precipitated using methanol (sample C) and a50--50 acetone/methanol mixture (sample D). The respective samples (B-D)were dried and then washed with acetone utilizing about 4 parts ofacetone, per 1 part of sample. All of the samples were then analyzed byliquid chromatography to determine the percent by weight of cyclics. Thefollowing results were obtained, where "IV" is intrinsic viscosity inchloroform at 25° C. and "% Cyclics (after acetone wash)" represents thepercent by weight of cyclic aromatic polyformal, based on the totalweight of the sample.

    ______________________________________                                                                      % Cyclics (after                                Sample   IV     % Cyclics     acetone wash)                                   ______________________________________                                        A               7.8                                                           B        0.62   6.6           4.7                                             C        0.61   2.2           1.4                                             D        0.61   1.6            0.98                                           ______________________________________                                    

The above results show that the original aromatic polyformal A had 7.8%cyclics. The direct precipitation of the sample into methanol, sample B,improved the product slightly, while the reverse precipitation effecteda significant removal of cyclics.

EXAMPLE 3

A mixture of 453.5 parts of bisphenol-A, 4.59 parts ofp-tert-butylphenol, 825 part of reagent grade methylene chloride and 966parts of N-methylpyrrolidone was stirred under nitrogen until ahomogeneous solution was obtained. There was then added 169.8 parts of97% sodium hydroxide pellets under a nitrogen blanket and the mixtureexothermed to 37° C. The mixture was then refluxed for 5 hours. Afterhour 1 hour, a considerble amount of a white precipitate began to formand a slight increase in viscosity was noted. After a 2 hour period, thereaction mixture was very viscous. Aliquots were removed after 3 and 4hours. At 5 hours, the mixture was cooled slightly and diluted withabout 8,800 parts of chlorobenzene to give a 5% solution.

The mixture was then allowed to cool to room temperature and settle overnight. The mixture was then filtered and the solids were washed with anadditional 1,600 parts of chlorobenzene during the filtration to producea 5% solution. The resulting filtrate was then acidified with aceticacid to produce a haze-free solution. While the polymer solution wasrapidly agitated, an equal volume of a methanol/acetone solution wasadded over a period of about 10 minutes. The walls of the blender werethen scraped and rinsed off and stirring continued for an additional 5minutes. This procedure was repeated until all of the solution had beentreated with the methanol/acetone solution. The resulting solid was thenfiltered and dried in a 65° C. vacuum oven. There was obtained a totalof 440.8 parts, a 96% yield, of a bisphenol-A polyformal, having anintrinsic viscosity of 0.565 in chloroform at 25° C. and consistingessentially of chemically combined units of the formula, ##STR3## andchain terminated with ##STR4##

A mixture of 429.8 parts of the above aromatic polyformal and about 1700parts of acetone was stirred for 20 minutes in an attempt to furtherreduce the cyclic level. There was obtained 410.41 parts of bisphenolpolyformal having an intrinsic viscosity of 0.57 and a cyclic content of0.78%, based on liquid chromatographic analysis.

The above polyformal was dissolved in methylene chloride to produce a10% solution. It was cast onto a glass substrate to produce a flexibletransparent film. A sample was injection molded to give a test samplehaving a Notched Izod Impact value of at least 1.0. Those skilled in theart would know that the polymer is a potentially useful engineeringthermoplastic having a variety of applications.

EXAMPLE 4

Example 3 was repeated, except that methylene chloride was substitutedfor chlorobenzene to dilute the reaction mixture. A solution wasfiltered through Celite on a glass frit and was then passed throughglass wool before the reverse precipitation step. There was obtained abisphenol-A polyformal having an intrinsic viscosity of 0.525 and 0.89%by weight cyclics and a T_(g) of 90° C. It was injection moldable andhad a Notched Izod Impact value of 1.

Although the above examples are directed to only a few of the very manyvariables which can be employed in the practice of the method of thepresent invention, it should be understood that the present invention isdirected to a much broader class of aromatic polyformals substantiallyfree of cyclic polyformals.

What we claim as new and desire to secure by Letters Patent of theUnited States is:
 1. A method for making a film forming aromaticpolyformal consisting essentially of chemically combined units of theformula,

    --OROCH.sub.2 --,

which is substantially free of aromatic polyformal in the cyclic statewhich comprises (A) agitating a mixture containing as essentialingredients bisphenol of the formula,

    HO--R--OH,

methylene halide, alkali metal hydroxide and a member selected from aphase transfer catalyst and dipolar aprotic solvent, where there isutilized in the reaction mixture, per mole of bisphenol, more than 1mole of methylene halide and greater than 2 moles of alkali metalhydroxide, (B) diluting the resulting mixture of (A) with an inertorganic solvent, (C) effecting the separation of solids from theresulting solution of (B) (D) while agitating the solution of (C),adding an antisolvent to the solution of (C), to effect theprecipitation of aromatic polyformal, and (E) effecting the recovery ofaromatic polyformal solids from (D) by a solid-liquid separation,where Ris a C.sub.(6-30) divalent aromatic radical.
 2. A method in accordancewith claim 1, wherein the bisphenol is 2,2-bis(4-hydroxyphenyl)propane.3. A method in accordance with claim 1, where the bisphenol is2,2'-(4-hydroxyphenyl)-1,1-dichloroethylene.
 4. A method in accordancewith claim 1, where the antisolvent is a mixture of methanol andacetone.
 5. A method in accordance with claim 1, where the dipolaraprotic solvent is N-methylpyrrolidone.
 6. A method in accordance withclaim 1, where the methylene halide is methylene chloride.
 7. A methodin accordance with claim 1, where there is utilized a chain-stopper inthe mixture of (A).
 8. A method in accordance with claim 1, where thearomatic polyformal is recovered as a high bulk density particulate. 9.A method in accordance with claim 1, where the recovered aromaticpolyformal is washed with additional antisolvent.
 10. A method formaking aromatic polyformal consisting essentially of chemically combinedunits of the formula, ##STR5## which comprises (F) agitating a mixturecontaining as essential ingredients bisphenol-A, methylene chloride,sodium hydroxide and N-methylpyrrolidone, where there is utilized in themixture, per mole of bisphenol-A, more than 1 mole of methylene chlorideand greater than 2 moles of sodium hydroxide,(G) diluting the resultingmixture of (F) with chlorobenzene, (H) filtering the resulting solutionof (G), (I) while agitating the resulting solution of (H), adding amethanol/acetone solution to effect the precipitation of the aromaticpolyformal and (J) recovering the aromatic polyformal of (I).